Full Mechanical: The Panel Telephone Switch

All about the sounds and workings of the telephone network. Let's start this off with the panel switch and how a basic intra-office call works. (That is, a call from a subscriber on a panel switch, to another subscriber on the same switch).

We'll show you how revertive pulse works, and what exactly is making all the noises you hear on the Phone Trips tapes. Make sure to leave a comment if you have any questions, and let me know if we should make more of these!

00:00 Intro & Explanation
2:35 Call through the Panel Switch
3:25 Battery & Dial Tone
6:20 Dialing
8:02 Decoder
9:40 How Selections Work
12:23 District Selections
17:20 Incoming Selections
20:32 Final Selections
23:10 Incoming Advance & Ringing
27:31 Review

[olduhfguy]

As a teenager I was invited to poke around in a working panel office. I didn't try to understand what was happening, but I was fascinated by all of the action !

[maxpeck]

I grew up around this stuff. My Dad was a lineman for Michigan Bell from 1965-1996. All of this takes me back to the late 70s/early 80s. Truly fascinating.

[itz_mxxri]

I've been in step by step offices, crossbar offices, and an ESS office, but I never thought I'd ever see a panel office. Let alone still in operation! Thank you for saving the only one left in the world!! But ironically, the oldest switch of all, the Strowger switch used in the SxS system, was also the one that was in service
longer than all of them!

[edgreenberg]

Makes me want to go back to my grandmother's home in Boro Park, Brooklyn, NY (718-436, or GEdney 6, as we knew it then) and listen again. I knew that her phone line was "different" but not exactly why. Calling into GE-6, from our Crossbar served line, we could hear the revertive pulsing coming back as the panel office soaked up the connection info. Grandma had a 300 set, which didn't have the same network as our 500 sets did, so the various clicks that came on call setup were much louder. It was fascinating then, and we didn't even have Sarah to explain it to us.

[GTCGreg]

So many open contacts and so much mechanics. It's a miracle any call got through at all. The maintenance on these machines must have been overwhelming.

[nateb]

This is breathtaking. A lot of the techs I worked with had stories from the panel days, but I never worked with anything older than a 1A ESS myself. You've just filled in so many gaps in my understanding!

I'm loving all the content on this channel so far, and I can't wait until I can come visit the museum in person.

[absurdengineering]

This is a masterwork in explaining complex concepts with just enough complexity included to make it accurate but not overwhelming. This video goes on my list of “when I grow up I want to make videos like this” :) Brilliantly done.

[mstrawn]

I worked on SXS, XY, DEX and DMS switches and had planned on visiting the last panel switch at Pacific Telephone in SFO but they ripped it right before I was able to go. At Bell System Private Line School, during the data section the mentioned that panel offices were notorious for impulse noise. I now understand why. Thank you! In the Army, our SXS and XY exchanges had end cells and end cell rectifiers. During high traffic, the end cells would cut in and add another 2V cell to the battery string. You could also tell when it was busy because the batteries would run down, so they wouldn't filter the 60 Hz hum from the rectifiers as well.

[lisamaginnis]

Evan Doorbell thanks you!

I rate this 2600 thumbs up!

[pigpenpete]

Nice work :) After listening to Evan Doorbell's tapes for ages this is helping to put the puzzle pieces together finally! More please!

[scanlime]

This is so good, thank you! I really appreciate the detailed breakdown and high quality recording, and your narration is always a joy.

[ds]

My grandmother’s line was on a step by step exchange, but my home phone in a different city was on a crossbar exchange. I used to notice when dialling home from my grandmother’s phone line I would hear the loud clicks of the equipment for the first 3 digits. After that, there were no background sounds for the final 4 digits being dialled, but as soon as I’d finish dialling the very last digits it would ring. There was never any delay. It was super fast with no audible clicks. When calling from my house to my grandmother’s house it was a very different sound because now I’m on a crossbar system calling into a step system. There were no noises at all on the crossbar when dialling until you reached the very last digit. You’d hear a double click. <click-click> and a pause and then another double click that was a lower volume and then it would ring. If I called my friend who was on the same crossbar exchange I would hear the same double clicks <click-click>, but then it would start ringing. No second set of clicks. I could be wrong but when calling my grandmother I always thought the crossbar system was sending the step system the last 4 digits and those had to be pulse dialled on the step side, which is why it would go quiet for 4 or 5 seconds before the second double clicks could be heard and the line would start ringing. I’ve always been intrigued with the sounds of the mechanical exchanges. I used them for so many decades that I was highly familiar with the audio routines they would go through, but this is the first time I ever saw what was going on to make those sounds. Thank you for showing us this Sarah. I loved this video. It was so educating. Thank you for the time you spent putting this excellent video together. It’s nice to know that the old mechanical stuff is still around. The phones make no sounds now with computers placing the calls these days and giving us artificial ring and busy tones generated by sound files. The old systems were more interesting and mysterious.

[zzco]

Nice to see people actually giving a crap about the technology Ma Bell invented. It's so fascinating how they pioneered this stuff, and how it was able to work automatically for nearly a century before digital circuitry came along and improved on it. I mean it makes sense HOW it all works, I'm still amazed by the WHY it's even able to work in the first place, y'know?

[KDNJR]

Amazing ! I didn’t understand everything, but I see and hear database queries and state machines and logic, feedback loops ... all done with mechanical elements !

[ManyManyPandas]

I would love to hear #1 Crossbar next. I just love hearing those Register Senders clicking away once you finish dialing. There's a certain charm that only #1 Crossbar has.

[paulkocyla]

The central office battery supply is calling for MAMA. Formants forming.
Or did it go sentient - DAM DAM DAM! No seriously, your deep understanding of every aspect of this system is amazing! Thanx for the explanation. It´s a treasure. I don´t know where else you could find this information in this quality! You´re awesome!

[joe]

Amazing video. Brings a whole different level of detail to all those Evan Doorbell tapes. Thank you!

[summersky]

"That's three clicks for incoming brush two: 0, 1, 2 Stop!"
Astrid, I absolutely love your dedication to this! You're just amazing!!! Thank-you, for people like you. Loved this video...even watched it a second and now a third time. Fascinating stuff. :) Love how you present this with so much passion and beauty.

[jessicam.]

Such great detail and explanations of such a complex machine. I'm definitely looking forward to more!

[RSCuber]

The panel has to be my favorite switch, I think. They are mechanical marvels and I just love the sound of panel pulses. Thanks for explaining these as well as you do. 🙂